The instant invention relates to propfan propulsion systems. More specifically, the invention relates to a propfan propulsion system on a small cruise missile utilizing two counter-rotating foldable blades.
Theoretical studies and test data indicate that propfan engines may improve fuel efficiency by 15-30%. However, for small missile applications, the propeller has an effective diameter much larger than that of the missile, making propfan powered missiles difficult to store and launch. A design is needed for a propeller blade which can be folded for storage and launching, and deployed for propulsion once airborne. Moreover, it is desirable to have two counter-rotating sets of blades to further increase fuel efficiency. Unfortunately, it is difficult to deploy the blades of counter-rotating hubs because the blades of one hub may interfere with the blades of another if the hubs begin to rotate during deployment.
The prior art teaches a propfan utilizing foldable blades which can be deployed for propulsion means upon operator command, as shown in U.S. Pat. No. 3,957,229, issued on May 18, 1976 to Davis. More specifically, Davis teaches blades which are hinged onto an annular hub and deployed via centrifugal force when the hub begins to rotate. The blades are spring biased towards the folded position. Thus, if the hub is held motionless, the blades will not deploy. Unfortunately, although the blades taught by Davis can be folded against a missile housing, missiles utilizing such blades would still be difficult to store and launch because the blades are exposed. In addition, since Davis teaches one hub and set of blades, he fails to teach a means for preventing interference between the blades of different hubs during deployment.
The prior art teaches a means for covering foldable projections during storage and launch. For example, in U.S. Pat. No. 4,565,340, issued Jan. 21, 1986, Baines teaches a projectile having guidance fins which are held in an axial position by an external casing until the projectile is launched from the casing, whereupon the blades spring out to a radially extended position. Nonetheless, since Baines is not concerned with using the guidance fins for propulsion, he also fails to teach a means for preventing interference between the blades of different hubs during deployment.
The prior art also teaches propfan propulsion systems using two counter-rotating blades, as shown, for example, in British Patent No. 601,170, issued Apr. 29, 1948 to Smith. However, Smith teaches permanently deployed blades such as those which might be used on a larger aircraft. Thus Smith is not faced with, nor does he offer a solution to, the problem of interference between the blades of different hubs during deployment.